Though three different actors have played Bruce Banner on the big screen in the past decade, only one can really say he also played the Hulk. When Mark Ruffalo appeared as the iconic character in last summer’s The Avengers, he was the first actor to actually portray the Hulk half of the character in motion-capture. (His predecessors Edward Norton and Eric Bana let the CG artists take over that part.)

The decision paid off, as fans enthused that Ruffalo’s Hulk was the best they’d seen in recent memory. Now a new video shows just how Industrial Light & Magic pulled off the trick. Hit the jump to check it out.

First founded by George Lucas in the ’70s for Star Wars, ILM has been behind some of the most notable cutting-edge effects work of the past few decades. Last year alone, they contributed work to Red Tails, The Hunger Games, Battleship, Cloud Atlas, and Paranormal Activity 4, in addition to The Avengers. Grantland posted this video from their studios.

No matter how often I watch these behind-the-scenes videos, I’m always startled by the massive difference between what I saw in the theaters (i.e., the Hulk stomping around Manhattan) and what was actually filmed on set (i.e., Ruffalo in a goofy hat prancing around a green-walled room).

As we’ve said before, part of the “problem” with VFX is that the really good work is so seamlessly done it’s easy not to notice it at all. But videos like this one demonstrate just how much skill and labor have to go into making scenes like this one work — and, unfortunately, the recent VFX protests highlight just how badly these talented artists are treated in return.